Amplifier, radiation detector, and radiation detector control method

ABSTRACT

The circuit area of an amplifier provided in a photon-counting radiation detector is decreased compared with the related art. A pulse amplification measurement circuit includes: an inverting amplification circuit that inverts and amplifies an input signal to generate an inverted amplified output; a feedback transistor that connects an input unit and an output unit of the inverting amplification circuit to each other; and a pulse measurement circuit that generates an output signal corresponding to the number of pulses of the inverted amplified output. The pulse measurement circuit is capable of supplying the output signal toward the feedback transistor.

TECHNICAL FIELD

An aspect of the present invention relates to an amplifier provided in aphoton-counting radiation detector.

BACKGROUND ART

In recent years, various techniques for measuring radiation (forexample, X-rays) have been developed. For example, a photon-countingradiation detector that detects radiation by counting the number ofphotons of the radiation incident on the photon-counting radiationdetector has been developed.

The photon-counting radiation detector has a configuration including acombination of (i) a sensor element that outputs an electrical signalcorresponding to the number of photons of the radiation and (ii) anamplifier formed of transistors (for example, a complementary metaloxide semiconductor (CMOS) integrated circuit). In the photon-countingradiation detector, the electrical signals received from the sensorelement are amplified by the amplifier and pulses are generated, and thenumber of generated pulses is counted for a predetermined time to detectthe radiation.

As an example, Patent Literature 1 discloses a technique for configuringan amplifier using transistors other than metal oxide semiconductorfield effect transistors (MOSFETs) in a photon-counting radiationdetector. According to the technique of Patent Literature 1, forexample, thin film transistors (TFTs) can be used as the transistors ofthe amplifier.

More specifically, the amplifier of Patent Literature 1 is provided witha regulator circuit for regulating a voltage applied to a controlterminal (gate) of a feedback transistor so that as inverter group doesnot oscillate. The regulator circuit includes an oscillation detectorand a ramp generator. By providing the regulator circuit, a transistorother than a MOSFET (for example, a TFT) can be applied to theamplifier.

CITATION LIST Patent Literature

PTL 1: Japanese Unexamined Patent Application Publication No.2016-152613 (published on Aug. 22, 2016)

SUMMARY OF INVENTION Technical Problem

However, in the technique of Patent Literature 1, it is necessary toindividually provide the regulator circuit including the oscillationdetector and the ramp generator for each amplifier. Accordingly, thereis a problem that the circuit area of the amplifier is increased. Anaspect of the present invention is to decrease the circuit area or anamplifier provided in a photon-counting radiation detector compared withthe related art.

Solution to Problem

To solve the problem, an amplifier according to an aspect of the presentinvention is an amplifier provided in a photon-counting radiationdetector, and includes: an inverting amplification unit that inverts andamplifies an input signal to generate an inverted amplified output; afeedback transistor that connects an input unit and an output unit ofthe inverting amplification unit to each other; and a pulse measurementunit that generates an output signal corresponding to a number of pulsesof the inverted amplified output, in which the pulse measurement unit iscapable of supplying the output signal toward the feedback transistor.

Advantageous Effects of Invention

According to an amplifier of an aspect of the present invention, it ispossible to decrease circuit area compared with the related art.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram schematically illustrating a configuration of apulse amplification measurement circuit according to Embodiment 1.

FIG. 2 is a diagram schematically illustrating a configuration of thepulse measurement circuit in FIG. 1.

FIG. 3 is a diagram illustrating an example of a change in each voltagein the pulse amplification measurement circuit of FIG. 1.

FIG. 4 is a diagram schematically illustrating a configuration of apulse amplification measurement circuit according to Embodiment 2.

FIG. 5 is a diagram illustrating an example of a change in each voltagein the pulse amplification measurement circuit of FIG. 4.

FIG. 6 is a diagram schematically illustrating a configuration of apixel according to Embodiment 3.

FIG. 7 is a diagram schematically illustrating a configuration of aradiation detector according to Embodiment 3.

DESCRIPTION OF EMBODIMENTS Embodiment 1

Hereinafter, Embodiment 1 is described in detail with reference to FIGS.1 to 3. Further, in the following description, a description of mattersthat are not related to Embodiment 1 is omitted as appropriate. It maybe understood that each member of a pulse amplification measurementcircuit 1 (amplifier) of Embodiment 1 whose description is omitted issimilar to that of a well-known technique.

(Pulse Amplification Measurement Circuit 1)

FIG. 1 is a diagram schematically illustrating a configuration of apulse amplification measurement circuit 1. The pulse amplificationmeasurement circuit 1 includes an inverting amplification circuit 10(inverting amplification unit), a pulse measurement circuit 11 (pulsemeasurement unit), a voltage sweep circuit 12 (voltage sweep unit), aswitch 13, and transistors T1 to T3.

The inverting amplification circuit 10 includes three invertingamplifiers 15 a to 15 c. Further, an analog-to-digital converter (ADC)14 is provided outside the pulse amplification measurement circuit 1.The ADC 14 may be provided in a radiation detector 300 to be describedlater.

The voltage sweep circuit 12 and the transistors T1 to T3 maycollectively be referred to as a regulator circuit. The transistors T2(second transistor) and T3 (third transistor) may be referred to as anoscillation interlock switch and a potential fixing switch,respectively. The transistor T1 (feedback transistor) may be referred toas a feedback switch. The transistor T1 functions similarly to thefeedback transistor in Patent Literature 1.

In addition, FIG. 2 is a diagram schematically illustrating aconfiguration of the pulse measurement circuit 11. The pulse measurementcircuit 11 includes transistors T4 and T5 and a capacitor Ci. Since theconfiguration and operation of the pulse measurement circuit 11 areknown, description thereof is omitted.

The transistors T1 to T5 function as switching elements. In Embodiment1, similar to Patent Literature 1, each transistor in the pulseamplification measurement circuit 1 may be, for example, a thin filmtransistor (TFT). However, each transistor may be a transistor otherthan the TFT. Each transistor may be any type of field effect transistor(FET).

In Embodiment 1, a case where the transistors T1 to T5 are TFTs isexemplified. More specifically, a case where the transistors T1 to T5are n-type TFTs is exemplified. However, the transistors T1 to T5 may hep-type TFTs. In addition, the switch 13 and the inverting amplificationcircuit 10 (inverting amplifiers 15 a to 15 c) may be TFTs.

An input signal In is supplied to the inverting amplification circuit 10of the pulse amplification measurement circuit 1 from a sensor element35 (not illustrated in FIG. 1) in FIG. 6 to be described later. Thesensor element 35 may be a known radiation sensor element. The sensorelement 35 generates an electrical signal (voltage pulse signal) as theinput signal In corresponding to the number of photons of radiation(more specifically, a radiation dose) incident on the sensor element.

The inverting amplification circuit 10 inverts and amplifies the inputsignal In to generate an amplified output signal AMPout (invertedamplified output). Therefore, the amplified output signal AMPout is avoltage pulse signal having a polarity opposite to that of the inputsignal In. An output terminal of the inverting amplification circuit 10is connected to the pulse measurement circuit 11 and the drain of thetransistor T1 (feedback transistor). The inverting amplification circuit10 outputs the amplified output signal AMPout to the pulse measurementcircuit 11.

The inverting amplification circuit 10 may be configured by connectingan odd number of inverting amplification circuits that invert andamplify a signal input thereto and output the amplified signal to eachother in series (in a cascading manner). In Embodiment 1, the invertingamplification circuit 10 includes the three inverting amplifiers 15 a to15 c. The number of inverting amplifiers provided in the invertingamplification circuit 10 may simply be an odd number and is notparticularly limited (see also FIG. 4, to be described later).

The amplification factor of the inverting amplification circuit 10 isdetermined by the number of inverting amplifiers. Therefore, to increasethe amplification factor of the inverting amplification circuit 10, thenumber of inverters may be increased. However, when the number ofinverters is increased, the inverting amplification circuit 10 (morespecifically, a feedback control system in the pulse amplificationmeasurement circuit 1) becomes unstable, such that oscillation easilyoccurs in the inverting amplification circuit 10. Therefore, it ispreferable that the number of inverting amplifiers be set inconsideration of the amplification factor and stability of the invertingamplification circuit 10.

The pulse measurement circuit 11 receives the amplified output signalAMPout. The pulse measurement circuit 11 is a circuit for measuring(counting) the number of pulses of the amplified output signal AMPout.Specifically, an output signal Out of the pulse measurement circuit 11is used as an index of the number of pulses of the amplified outputsignal AMPout.

A reset signal Reset is supplied to the pulse measurement circuit 11 andthe voltage sweep circuit 12. The reset signal Reset may be suppliedfrom a control circuit 31 to be described later to each of the pulsemeasurement circuit 11 and the voltage sweep circuit 12 (see also FIG.7).

In the pulse measurement circuit 11, the reset signal Reset is used as asignal for initializing the value (voltage value) of the output signalOut. Specifically, in a case where the reset signal Reset (a pulse ofthe reset signal Reset) having a high level value is input to the pulsemeasurement circuit 11, the output signal Out is initialized a highlevel value (maximum value) (hereinafter, referred to as a voltageVHIGH).

Next, the pulse measurement circuit 11 generates the output signalcorresponding to the number of pulses of the amplified output signalAMPout. More specifically, the pulse measurement circuit 11 decreasesthe value of the output signal Out by a predetermined value each timeone pulse of the amplified output signal AMPout is input to the pulsemeasurement circuit 11. Therefore, it is possible to measure the numberof pulses of the amplified output signal AMPout (that is, the number ofpulses of the input signal In) by measuring how much the value of theoutput signal Out is decreased from VHIGH.

The switch 13 switches a supply destination of the output signal Outoutput from the pulse measurement circuit to either the ADC 14 or thetransistor T2 (more specifically, the gate of the transistor T2). Byproviding the switch 13, the pulse measurement circuit 11 can output theoutput signal Out to either the outside or the inside of the pulseamplification measurement circuit 1.

First, as illustrated in FIG. 1, it is assumed that the switch 13supplies the output signal Out to the gate of the transistor T2. In thiscase, it may be understood that the pulse measurement circuit 11supplies the output signal Out toward the transistor T1.

Therefore, it may be understood that the switch 13 switches the supplydestination of the output signal Out either (i) toward the transistor T1(to the inside of the pulse amplification measurement circuit 1) or (ii)to the outside (the ADD 14) of the pulse amplification measurementcircuit 1.

In a case where the output signal Out is supplied toward the transistorT1, the pulse measurement circuit 11 is connected to the transistor T1through the transistors T2 and T3. More specifically, the pulsemeasurement circuit 11 connected to the gate of the transistor T2, andthe transistor T2 is connected to the gate of the transistor T1 throughthe transistor T3.

The pulse amplification measurement circuit 1 requires a period(regulating period) for regulating feedback resistance (resistancebetween the source and the drain of the transistor T1) of the invertingamplification circuit 10 before starting measurement of the pulse,similarly to the amplifier in Patent Literature 1. In the regulatingperiod, the switch 13 supplies the output signal Out to the gate of thetransistor T2. That is, the output signal Out is supplied to theregulator circuit described above.

The drain of the transistor T2 connected to the voltage sweep circuit12. The voltage sweep circuit 12 supplies a voltage Vramp (secondvoltage signal) to the drain of the transistor T2. In the voltage sweepcircuit 12, the reset signal Reset is used as a signal for initializinga value of the voltage Vramp.

Note that a case where the pulse amplification measurement circuit 1includes the voltage sweep circuit 12 is exemplified for convenience ofexplanation in Embodiment 1, but the voltage sweep circuit 12 is not anessential component of the pulse amplification measurement circuit 1.The voltage sweep circuit 12 may be provided outside the amplifieraccording to an aspect of the present invention (see Embodiment 3, to bedescribed later).

The voltage Vramp is a voltage that temporally increases at a constantrate from the value (minimum value) initialized by the reset signalReset. That is, the voltage Vramp is a voltage signal having a rampwaveform (inclined waveform) (see also FIG. 3, to be described later).

The source of the transistor T2 is connected to the drain of thetransistor T3. Therefore, the output signal Out supplied to the gate ofthe transistor T2 can be used as a signal for controlling switchon/switch off (conduction/non-conduction) of the transistor T2.

That is, a conduction state between the source and the drain of thetransistor T2 (in other words, a connection state between the voltagesweep circuit 12 and the drain of the transistor T3) can be controlledby the output signal Out. When the output signal Out is large to acertain extent, the transistor T2 is switched on, and the voltage Vrampcan thus be supplied from the voltage sweep circuit 12 to the drain ofthe transistor T3.

The source of the transistor T3 is connected to the gate of thetransistor T1. Hereinafter, a gate voltage of the transistor T1 isreferred to as a voltage Vg. A voltage Vwrt (third voltage signal) issupplied to the gate of the transistor T3. The voltage Vwrt may besupplied from a control circuit 31 to be described later to thetransistor T3 (see also FIG. 7).

The voltage Vwrt is a signal for controlling switch on/switch off of thetransistor T3. That is, the voltage Vwrt is a signal for controlling aconduction state between the source and the drain of the transistor T3(in other words, a connection state between the source of the transistorT2 and the gate of the transistor T1).

In a case where the voltage Vwrt is large to a certain extent, thetransistor T3 is switched on. Therefore, in a case where each of thevoltage Vwrt and the output signal Out is large to a certain extent, thetransistors T2 and T3 are switched on, and the voltage Vramp can thus besupplied from the voltage sweep circuit 12 to the gate of the transistorT1. In this case, the voltage Vg becomes equal to the voltage Vramp.

The source and the drain of the transistor T1 are connected to an inputside (input unit) and an output side (output unit) of the invertingamplification, circuit 10, respectively. That is, the transistor T1 is aswitching element connecting the input side and the output side of theinverting amplification circuit 10 to each other. In a case where thetransistor T1 is in a switch-on state, the transistor T1 causes theoutput (the amplified output signal AMPout) of the invertingamplification circuit 10 to feed back to the input side.

As illustrated in Patent Literature 1, it is preferable that theresistance value between the source and the drain of the transistor T1be as low as possible within a range in which the pulse amplificationmeasurement circuit 1 does not perform amplification. As describedabove, the resistance value between the source and the drain of thetransistor T1 decreases as the voltage Vg increases. Accordingly, it ispreferable that the voltage Vg be as high as possible within a range inwhich the pulse amplification measurement circuit 1 does not performamplification.

(Example of Change in Each Voltage in Pulse Amplification MeasurementCircuit 1)

FIG. 3 is a time chart illustrating an example of a change in voltage inthe pulse amplification measurement circuit 1. First, at time t0, thevoltage Vwrt is switched to a high level value, such that the transistorT3 is switched on.

Subsequently, at time t1, the reset signal Reset is switched to the highlevel value. As a result, the value of the output signal Out isinitialized to the voltage VHIGH (high level value), such that thetransistor T2 is switched on. Therefore, the voltage Vramp can besupplied from the voltage sweep circuit 12 to the gate of the transistorT1. That is, the voltage Vg can be made equal to the voltage Vramp.

The reset signal Reset is switched to the high level value at time t1,such that the voltage Vramp can be increased at a constant rate with thelapse of time. That is, the voltage Vg can be swept from a low voltageto a high voltage by the voltage Vramp. Therefore, the resistance valuebetween the source and the drain of the transistor T1 can decreaseaccording to an increase in the voltage Vg.

Next, at time t2, as the resistance value between the source and thedrain of the transistor T1 decreases, the oscillation starts in theinverting amplification, circuit 10. That is, the amplified outputsignal AMPout starts to oscillate. As a result, in accordance with theoscillation of the amplification output signal AMPout, the value of theoutput signal Out gradually decreases from VHIGH with the passage oftime. As such, the oscillation of the inverting amplification circuit 10can be detected by using the pulse measurement circuit 11 (by the outputsignal Out).

The voltage Vg increases so as to follow the voltage Vramp until time t3to be described later (that is, until the transistor T2 is switched off)even after time t2. Hereinafter, the voltage Vg at time t2 is referredto as a voltage Vgosc (oscillation start value). The voltage Vgosc is agate voltage at which the oscillation starts in the invertingamplification circuit 10.

The resistance value between the source and the drain of the transistorT1 at the voltage Vgosc (that is, the resistance value between thesource and the drain of the transistor T1 at which the oscillationstarts in the inverting amplification circuit 10) is referred to as anoscillation start feedback resistance value.

In addition, as time passes from time t2, the oscillation frequency ofthe amplified output signal AMPout increases in accordance with adecrease in the resistance value between the source and the drain of thetransistor T1. Accordingly, as illustrated in FIG. 3, the oscillationcycle of the amplified output signal AMPout is shortened with thepassage of time.

Thereafter, at time t3, when the value of the output signal Out reachesa low level value as the oscillation continues in the invertingamplification circuit 10, the transistor T2 is switched to a switch-offstate. The transistor T2 is switched off, such that the voltage Vg isheld at a voltage Vg1 (first value) at time t3. In addition, the voltageVg1 is held, such that the resistance value between the source and thedrain of the transistor T1 is also held at a constant value (firstfeedback resistance value) corresponding to the voltage Vg1. The firstfeedback resistance value is lower than the oscillation start feedbackresistance value.

The voltage Vg1 is a gate voltage at a point in time when the transistorT2 is switched to the switch-off state. As illustrated in FIG. 3, thevoltage Vg1 higher than the voltage Vgosc. Accordingly, the oscillationin the inverting amplification circuit 10 continues until time t4 to bedescribed later.

A parasitic capacitance of the transistor T1 and a parasitic capacitanceof each wiring in the pulse amplification measurement circuit 1contribute to the holding of the voltage Vg1. However, as illustrated inEmbodiment 2, to be described later, a capacitor Cm (memory capacitance)may be provided to hold the voltage Vg1.

After the voltage Vg is held at the voltage Vg1 the voltage Vwrt isswitched to the low level value at time t4, such that the transistor T3is switched off. As a result, at time t4, the voltage Vg is changed to avoltage Vg2 (second value) lower than the voltage Vg1 and the voltageVgosc described above as electric charge is extracted from the gate oftransistor T1 as described later.

As such, the voltage Vg is decreased to a voltage Vgp, such that theoscillation in the inverting amplification circuit 10 can be stopped attime t4. Since the oscillation is stopped after time t4, the voltage Vg2is stably held. The voltage Vg2 is held, such that the resistance valuebetween the source and the drain of the transistor TI is also held at aconstant value (second feedback resistance value) corresponding to thevoltage Vg2. The second feedback resistance value is higher than theoscillation start feedback resistance value.

Here, (i) the high level value of the voltage Vwrt (that is, the valueof the voltage Vwrt in a case where the transistor T3 is switched on) isVh, and (ii) the low level value of the voltage Vwrt (that is, the valueof the voltage Vwrt in a case where the transistor T3 is switched off)of the voltage Vwrt is V1. In addition, a capacitance between the gateand the source of the transistor T3 is Cgs. In addition, a capacitanceof the gate of the transistor T1 is Cg.

Next, a difference between the high level value and the low level valueof the voltage Vwrt (that is, the amount of change in the voltage Vwrt)is represented as ΔVwrt=Vh−V1. In addition, a difference between thevoltage Vg1 and the voltage Vg2 (that is, the amount of change in thevoltage Vg) is represented as Δvg=Vg1−Vg2.

In this case, the following Equation (1) is satisfied:

ΔVg=(Cgs/Cg)×ΔVwrt   (1).

That is, the voltage Vg2 is represented by the following Equation (2):

Vg2=Vg1−(Cgs/Cg)×ΔVwrt   (2).

Equations (1) and (2) mean that electric charge is extracted from thegate of the transistor T1 through the capacitance Cgs between the gateand the source of the transistor T3 by changing the voltage Vwrt.

As a result of such electric charge extraction, the voltage Vg (the gatevoltage of the transistor T3) is changed to the voltage Vg2 lower thanthe voltage Vg1. By appropriately setting the value of ΔVwrt, a desiredΔVg (in other words, Vg2) can be obtained. That is, a value of thevoltage Vg2 can be set to a value immediately before the oscillationstarts in the inverting amplification circuit 10 (a value sufficientlyclose to the voltage Vgosc at which the oscillation starts)(hereinafter, referred to as a value immediately before theoscillation). In addition, the value of the voltage Vg2 can also be setby regulating the increase rate of the voltage Vramp.

By setting the voltage Vg2 to the value immediately before theoscillation by such regulation, the regulating period described aboveends. By setting the voltage Vg2 to the value immediately before theoscillation, the resistance value between the source and the drain ofthe transistor T1 can be made sufficiently low within a range in whichthe inverting amplification circuit 10 does not oscillate.

When the regulating period ends, the supply destination of the outputsignal Out is switched to the ADC 14 by the switch 13. As describedabove, the output signal Out is an analog value whose value (voltage)decreases in accordance with the measurement of the number of pulses ofthe input signal In.

By the ADC 14 converting the output signal Out (analog value) into adigital value, the number of pulses of the input signal In can bemeasured more simply. The subsequent processing for measuring the numberof pulses is known, and description thereof is thus omitted.

(Effect of Pulse Amplification Measurement Circuit 1)

According to the pulse amplification measurement circuit 1, it ispossible to cause the pulse measurement circuit 11 to supply the outputsignal Out toward the transistor T1 by the switch 13. Then, asillustrated in FIG. 3 described above, the voltage Vg (the gate voltageof the transistor TI) can be regulated so that the invertingamplification circuit 10 does not oscillate. In other words, theresistance value between the source and the drain of the transistor T1can be regulated so that the inverting amplification circuit 10 does notoscillate.

That is, the voltage Vg can be regulated without providing the regulatorcircuit (the regulator circuit including the oscillation detector andthe ramp generator) of Patent Literature 1. Therefore, unlike in PatentLiterature 1, there is no need to individually provide the regulatorcircuit for the amplifier (pulse amplification measurement circuit 1).

Therefore, the circuit area of the amplifier provided in thephoton-counting radiation detector can be decreased compared with therelated art. Furthermore, the circuit area of a radiation detector (forexample, a radiation detector 300 to be described later) including theamplifier can also be decreased.

Embodiment 2

Embodiment 2 is described below with reference to FIGS. 4 and 5. Forconvenience of explanation, members having the same functions as thoseof the members described in the above embodiment are denoted by the samereference numerals, and description thereof is omitted.

(Pulse Amplification Measurement Circuit 2)

FIG. 4 is a diagram schematically illustrating a configuration of apulse amplification measurement circuit 2 (amplifier) according toEmbodiment 2. The pulse amplification measurement circuit 2 has aconfiguration in which (i) the inverting amplification circuit 10 in thepulse amplification measurement circuit 1 is replaced by an invertingamplification circuit 20 (inverting amplification unit) and (ii) anamplifier 21, a buffer 22, a capacitor Ca, and a capacitor Cm are added.In FIG. 4, illustration of the switch 13 and the ADC 14 is omitted forconvenience of explanation. The same applies to FIGS. 6 and 7 to bedescribed later.

The inverting amplification circuit 20 is different from the invertingamplification circuit 10 in that the inverting amplification circuit 20includes only one inverting amplifier 15 a. In the pulse amplificationmeasurement circuit 2, an output side of the inverting amplificationcircuit 20 and an input side of a pulse measurement circuit 11 areconnected to each other through the amplifier 21.

The amplifier 21 may be a known non-inverting amplifier. In the pulseamplification measurement circuit 2, an amplified output signal AMPoutis further amplified by the amplifier 21, and the amplified outputsignal AMPout after being amplified is input to the pulse measurementcircuit 11.

In the pulse amplification measurement circuit 2, an output side of thepulse measurement circuit 11 and the gate of a transistor T2 areconnected to each other through the buffer 22. The amplifier 21 may be aknown buffer. In the pulse amplification measurement circuit 2, anoutput signal Out is further amplified by the buffer 22, and theamplified output signal Out is input to the gate of the transistor T2.

Note that, in the pulse amplification measurement circuit 2, theamplifier 21 and the buffer 22 are not essential components. Forexample, similarly to the pulse amplification measurement circuit 1, ina case of using the inverting amplification circuit 10 (invertingamplification unit) including the three inverting amplifiers 15 a to 15c, the amplification factor of the inverting amplification unit issufficiently high, and the amplifier 21 and the buffer 22 can thus beomitted.

One terminal of the capacitor Ca is connected to each of the source ofthe transistor T2 and the drain of the transistor T3. That is, oneterminal of the capacitor Ca is connected to the transistor T1 throughthe transistor T3. A voltage Vadj (fourth voltage signal) is input tothe other terminal of the capacitor Ca. The voltage Vadj may be suppliedfrom, for example, the control circuit 31.

Electric charge can be injected into the capacitor Ca by applying avoltage Vadj having a high level value to the capacitor Ca. Thus, thecapacitor Ca may be referred to as electric charge injectioncapacitance. In addition, the electric charge can be extracted from thecapacitor Ca by applying a voltage Vadj having a low level value to thecapacitor Ca.

One terminal of the capacitor Cm is connected to each of the source ofthe transistor T3 and a gate of the transistor T1. The other terminal ofthe capacitor Cm is grounded. The capacitor Cm is provided for thepurpose of holding the voltage Vg (the gate voltage of the transistorT1) described above. The capacitor Cm may be referred to as memorycapacitance.

(Example of Change in Each Voltage in Pulse Amplification MeasurementCircuit 2)

FIG. 5 is a time chart illustrating an example of a change in eachvoltage the pulse amplification measurement circuit 2. In FIG. 5, thevoltage Vadj is further illustrated, in addition to each voltageillustrated in FIG. 3. A change in each voltage and operation of eachmember from time t0 to time t3 are similar to those of FIG. 3, anddescription thereof is thus omitted.

To distinguish FIG. 5 from FIG. 3, in FIG. 5, a time when oscillation isstopped in the inverting amplification circuit 20 is represented as timet5. As illustrated in FIG. 5, the voltage Vadj is set to a high levelvalue from time t0 to time t5.

In the pulse amplification measurement circuit 2, at time t5, thevoltage Vadj is switched to a low level value. As electric charge isextracted from the capacitor Ca by the voltage Vadj having the low levelvalue, the electric charge is extracted from the gate of the transistorT1. As a result, the voltage Vg decreases from the voltage Vg1 (firstvalue) to the voltage Vgp (third value). Here, the voltage Vgp is lowerthan the voltage Vgosc described above. Therefore, the oscillation canbe stopped in the inverting amplification circuit 20 by decreasing thevoltage Vg to the voltage Vgp. The voltage Vgp is held until time t6 tobe described later.

A resistance value between the source and the drain of the transistor T1at the voltage Vgp is referred to as a third feedback resistance value.The third feedback resistance value is higher than the oscillation startfeedback resistance value.

As such, in the pulse amplification measurement circuit 2, the voltageVg is decreased by the extraction of the electric charge from thecapacitor Ca according to the change in the voltage Vadj. That is, inthe pulse amplification measurement circuit 2, the voltage Vg can bedecreased by an operation different from that of the pulse amplificationmeasurement circuit 1.

Here, the high level value of the voltage Vadj is Vadjh, and (ii) thelow level value of the voltage Vwrt is Vadjl. In addition, thecapacitance of the capacitor Ca and the capacitance of the capacitor Cmare represented as Caux and Cmem, respectively.

Next, a difference between the high level value and the low level valueof the voltage Vadj (that is, the amount of change in the voltage Vadj)is represented as ΔVadj=Vadjh−Vadj1. In addition, a difference betweenthe voltage Vg1 and the voltage Vgp (that is, the amount of change inthe voltage Vg) is represented as ΔVg2=Vg1−Vgp.

In this case, the following Equation (2) is satisfied:

ΔVg2=(Caux/Cmem)×ΔVadj   (3).

That is, the voltage Vgp is represented by the following Equation (3):

Vgp=Vg1−(Caux/Cmem)×ΔVadj   (4).

As an example, in a case where Caux/Cmem=1 and ΔVadj=0.1 V, ΔVgp=0.1 V.That is, a voltage Vgp lower than the voltage Vg1 by 0.1 V can beobtained. By appropriately setting values of Caux/Cmem and ΔVadj, adesired ΔVg2 (in other words, Vgp) can be obtained.

Thereafter, at time t6, similarly to the abovementioned time t4 (seeFIG. 3), the voltage Vwrt is switched to the low level value, such thatthe transistor T3 is switched off. As a result, similarly to the pulseamplification measurement circuit 1, the voltage Vg further decreasesfrom Vgp to become a voltage Vg2. After time t6, the voltage Vg2 isheld.

As such, the voltage Vg can also be regulated by the pulse amplificationmeasurement circuit 2 so that the inverting amplification circuit 20does not oscillate. Therefore, an effect similar to that of Embodiment 1can be obtained.

Embodiment 3

Embodiment 3 is described below with reference to FIGS. 6 and 7. InEmbodiment 3, a pixel 30 and a radiation detector 300 each including anamplifier according to an aspect of the present invention are described.

(Pixel 30)

FIG. 6 is a diagram schematically illustrating a configuration of thepixel 30. The pixel 30 in Embodiment 3 includes (i) a sensor element 35and (ii) each unit of the pulse amplification measurement circuit 1excluding the voltage sweep circuit 12. However, in the pixel 30, theconfiguration of the pulse amplification measurement circuit 2 may beapplied instead of the configuration of the pulse amplificationmeasurement circuit 1.

As described above, in the pixel 30, the sensor element 35 generates aninput signal In as an index of a dose of the radiation detected thesensor element. Then, in the pulse amplification measurement circuit 1,it is possible to generate the output signal Out on the basis of theinput signal In. As such, the pixel 30 is the smallest unit (detectionunit) for detecting the dose of the radiation.

(Radiation Detector 300)

FIG. 7 is a diagram schematically illustrating a configuration of aphoton-counting radiation detector 300. The radiation detector 300includes a plurality of (for example, four) pixels 30, a voltage sweepcircuit 12, and a control circuit 31. In the radiation detector 300, ina case where the pixels 30 are one-dimensionally (for example, linearly)arranged, a unit group capable of one-dimensionally detecting (imaging)radiation can be configured.

Alternatively, in the radiation detector 300, in a case where the pixels30 are arranged two-dimensionally (for example, in a matrix form in arow direction and a column direction), a unit group capable of detectingradiation two-dimensionally can be configured. As such, the pixels 30may be arranged according to any spatial pattern, depending on the useof the radiation detector 300.

The control circuit 31 generally controls each unit of the radiationdetector 300. As described above, the control circuit 31 supplies areset signal Reset and a voltage Vwrt to each of the plurality of pixels30 (in other words, each of a plurality of pulse amplificationmeasurement circuits 1).

In FIG. 7, a configuration in which the four pixels 30 share one voltagesweep circuit 12 with one another is exemplified. Accordingly, in theradiation detector 300, the voltage sweep circuit 12 supplies thevoltage Vramp to each of the plurality of pixels 30. As such, by causingthe plurality of pixels 30 to share the voltage sweep circuit 12 withone another, the circuit area of the radiation detector 300 can befurther decreased.

In the radiation detector 300, a plurality of voltage sweep circuits 12may be provided. If two or more pixels 30 of the plurality of pixels 30share one voltage sweep circuit with each other, the circuit area of theradiation detector 300 can be decreased. However, to more effectivelydecrease the circuit area of the radiation detector 300, it ispreferable that all of the plurality of pixels 30 share one voltagesweep circuit 12 with one another.

In the radiation detector 300, a mode of counting the number of photonsof radiation to detect radiation is referred to as a first mode(counting mode). As an example, in the pulse amplification measurementcircuit 1 of FIG. 1, in a case where the pulse measurement circuit 11 isconnected to the ADC 14 by the switch 13, the radiation detector 300 canbe operated in the first mode.

In addition, in the radiation detector 300, a mode of regulating afeedback resistance value (a resistance value between the source and thedrain of the transistor T1) of the inverting amplification circuit 10 isreferred to as a second mode (regulating mode). As an example, in thepulse amplification measurement circuit 1, in a case where the pulsemeasurement circuit 11 is connected to the gate of the transistor 2 bythe switch 13, the radiation detector 300 can be operated in the secondmode.

As such, the radiation detector 300 can be operated in any one of thefirst mode and the second mode. Therefore, an operation method (controlmethod) of the radiation detector 300 may include a first step ofoperating the radiation detector 300 in the first mode and a second stepof operating the radiation detector 300 in the second mode.

Next, as understood from Embodiment 1 (particularly FIG. 3) describedabove, the second step may further include (i) a step of decreasing thefeedback resistance value so that the inverting amplification circuit 10is shifted from a state where it does not oscillate to a state in whichit does oscillate, (ii) a step of detecting that the invertingamplification circuit 10 oscillates by using the pulse measurementcircuit 11, (iii) a step of holding the feedback resistance value at afirst feedback resistance value (feedback resistance value at which theoscillation of the inverting amplification circuit 10 continues), and(iv) a step of increasing the feedback resistance value from the firstfeedback resistance value to a second feedback resistance value(feedback resistance value at which the oscillation of the invertingamplification circuit 10 does not occur) and holding the second feedbackresistance value.

[Overview]

An amplifier (pulse amplification measurement circuit 1) according to afirst aspect of the present invention is an amplifier provided in aphoton-counting radiation detector (300) and includes an invertingamplification unit (inverting amplification circuit 10) that inverts andamplifies an input signal (In) to generate an inverted amplified output(Ampout), a feedback transistor (transistor T1) that connects an inputunit and an output unit of the inverting amplification unit to eachother, and a pulse measurement unit (pulse measurement circuit 11) thatgenerates an output signal (Out) corresponding to the number of pulsesof the inverted amplified output, in which the pulse measurement unit iscapable of supplying the output signal toward the feedback transistor.

According to the above configuration, it is possible to cause the pulsemeasurement circuit 11 to supply the output signal toward the feedbacktransistor. Therefore, for example, as illustrated in FIG. 3 describedabove, a gate voltage (voltage Vg) of the feedback transistor canregulated so that the inverting amplification unit does not oscillate.

Therefore, unlike Patent Literature 1, the voltage Vg can be regulatedwithout providing the regulator circuit (the regulator circuit includingthe oscillation detector and the ramp generator) of Patent Literature 1.Therefore, the circuit area of the amplifier can be decreased comparedwith the related art.

According to a second aspect of the present invention, preferably theamplifier according to the first aspect may further include a switch(13) that switches a supply destination of the output signal from thepulse measurement unit either (i) toward the feedback transistor or (ii)to the outside of the amplifier.

According to the above configuration, it is possible to cause the pulsemeasurement circuit 11 to supply the output signal toward the feedbacktransistor by switching the switch.

According to a third aspect of the present invention, in the amplifieraccording to the first or second aspect, preferably in a case where thepulse measurement unit supplies the output signal toward the feedbacktransistor, the pulse measurement unit is connected to a gate of asecond transistor (T2), the second transistor is connected to a gate ofthe feedback transistor through a third transistor (T3), at a point intime before the inverting amplification unit oscillates, the secondtransistor and the third transistor are switched on and a gate voltage(Vg) of the feedback transistor increases according to a second voltagesignal supplied to the second transistor, at a point in time when thegate voltage of the feedback transistor reaches an oscillation startvalue (Vgosc), the inverting amplification unit may start to oscillate,at a point in time after the inverting amplification unit starts tooscillate, the gate voltage of the feedback transistor may be held at afirst value (Vg1) larger than the oscillation start value by switchingoff the second transistor as the oscillation of the invertingamplification unit continues, and at a point in time after the gatevoltage of the feedback transistor is held at the first value, the gatevoltage of the feedback transistor may be held at a second value (Vg2)smaller than the oscillation start value by extracting electric chargefrom the feedback transistor in accordance with a change in a thirdvoltage signal supplied to the third transistor.

As described above, preferably the voltage Vg may be sufficiently highwithin the range in which the inverting amplification unit does notoscillate. According to the above configuration, the voltage Vg can beheld at the second value (Vg2) at which the oscillation of the invertingamplification unit does not occur. Accordingly, the voltage Vg can beregulated, for example, by controlling the amount of change in the thirdvoltage signal and setting the second value to the value (valuesufficiently close to Vgosc) immediately before the oscillation.

According to a fourth aspect of the present invention, the amplifieraccording to the third aspect may further include a capacitor (Ca), inwhich one terminal of the capacitor is connected to the feedbacktransistor through the third transistor, a fourth voltage signal(voltage Vadj) is supplied to another terminal of the capacitor, and atthe point in time after the gate voltage of the feedback transistor isheld at the first value, the gate voltage of the feedback transistor isheld at a third value smaller than the oscillation start value byextracting electric charge from the feedback transistor in accordancewith a change in the fourth voltage signal.

According to the above configuration, the voltage Vg can be held at thethird value (Vg3) at which the oscillation of the invertingamplification unit does not occur. Therefore, the voltage Vg can also beregulated by this configuration.

A radiation detector according to a fifth aspect of the presentinvention may preferably include amplifier according to any one of thefirst to fourth aspects and a sensor element (35) that generates theinput signal corresponding to a dose of radiation incident on the sensorelement.

According to the above configuration, an effect similar to that of theamplifier according to an aspect of the present invention is obtained.

According to a sixth aspect of the present invention, preferably theradiation detector according to the fifth aspect may include a pluralityof amplifiers each of which is the amplifier according to any one of thefirst to fourth aspects and one or more voltage sweep units (voltagesweep circuits 12) that output a second voltage signal increasing a gatevoltage of the feedback transistor at a point in time before theinverting amplification unit oscillates and two or more amplifiers ofthe plurality of the amplifiers may share one of the one or more voltagesweep units with each other.

According to the above configuration, the circuit area of the radiationdetector can be more effectively decreased.

According to a seventh aspect of the present invention, in the radiationdetector according to the sixth aspect, preferably all of the pluralityof the amplifiers may share the one voltage sweep unit with one another.

According to the above configuration, the circuit area of the radiationdetector can be more effectively decreased.

A radiation detector control method according to an eighth aspect of thepresent invention is a radiation detector control method for controllingthe radiation detector according to any one of the fifth to seventhaspects and may preferably include a first step of operating theradiation detector in a first mode of counting a number of photons ofthe radiation to detect the radiation by switching the supplydestination of the output signal from the pulse measurement unit towardthe feedback transistor and a second step of operating the radiationdetector in a second mode of regulating the feedback resistance value ofthe inverting amplification unit by switching the supply destination ofthe output signal from the pulse measurement unit to the outside of theamplifier.

According to the above configuration, an effect similar to that of theamplifier according to an aspect of the present invention is obtained.

According to a ninth aspect of the present invention, in the radiationdetector control method according to the eighth aspect, preferably thesecond step may further include a step of decreasing the feedbackresistance value so that the inverting amplification unit is shiftedfrom a state where the inverting amplification unit does not oscillateto a state in which the inverting amplification unit does oscillate, astep of detecting that the inverting amplification unit oscillates byusing the pulse measurement unit, a step of holding the feedbackresistance value at a first feedback resistance value at which theoscillation of the inverting amplification unit continues, and a step ofincreasing the feedback resistance value from the first feedbackresistance value to a second feedback resistance value at which theoscillation of the inverting amplification unit does not occur andholding the second feedback resistance value.

According to the above configuration, an effect similar to that of theamplifier according to an aspect of the present invention is obtained.

[Appendix]

An aspect of the present invention is not limited to the embodimentsdescribed above and various modifications can be made within the scopeof the claims, and embodiments obtained by appropriately combiningtechnical means disclosed in different embodiments with each other arealso included in the technical scope of an aspect of the presentinvention. Furthermore, new technical features can be formed bycombining technical means disclosed in each embodiment with each other.

[Other Expressions of Aspect of the Present Invention]

An aspect of the present invention can also be expressed as follows.

A pulse amplification measurement circuit according to an aspect of thepresent invention includes an inverting amplifier, a feedback transistorthat connects an input unit and an output unit of the invertingamplifier to each other, and a pulse measurement circuit that changes anoutput corresponding to a number of pulses output from the invertingamplifier, in which the pulse measurement circuit operates in a firststate in which a pulse signal amplified by the inverting amplifier iscounted and a second state in which oscillation of the invertingamplifier is detected.

In addition, pulse amplification measurement circuit according to anaspect of the present invention further includes a voltage sweeping unitthat changes a gate voltage of the feedback transistor, in which in thesecond state, an operation of changing the gate voltage of the feedbacktransistor and holding a gate voltage at a point in time whenoscillation of the inverting amplifier is detected and an operation ofreturning the gate voltage at the point in time when the oscillation ofthe inverting amplifier is detected to a gate voltage immediately beforethe inverting amplifier oscillates and holding the gate voltageimmediately before the inverting amplifier oscillates are performed.

In addition, the pulse amplification measurement circuit according to anaspect of the present invention performs the operation of returning thegate voltage at the point in time when the oscillation of the invertingamplifier is detected to a gate voltage immediately before the invertingamplifier oscillates by injecting a predetermined amount of electriccharge into an electrode to which the gate voltage is applied.

Further, the pulse amplification measurement circuit according to anaspect of the present invention includes a capacitance element connectedto the gate electrode and injects the electric charge into the gateelectrode by switching a voltage of a terminal of the capacitanceelement that is not connected to the gate electrode.

In addition, a radiation measurement instrument according to an aspectof the present invention includes a plurality of pulse amplificationmeasurement circuits according to an aspect of the present invention, inwhich two or more of the pulse amplification measurement circuits sharethe voltage sweep unit with each other.

REFERENCE SIGNS LIST

1, 2 Pulse amplification measurement circuit (amplifier)

10, 20 Inverting amplification circuit (inverting amplification unit)

11 Pulse measurement circuit (pulse measurement unit)

12 Voltage sweep circuit (voltage sweep unit)

13 Switch

35 Sensor element

300 Radiation detector

T1 Transistor (feedback transistor)

T2 Transistor (second transistor)

T3 Transistor (third transistor)

Ca Capacitor

In Input signal

Out Output signal

Vramp Voltage (second voltage signal)

Vwrt Voltage (third voltage signal)

Vadj Voltage (fourth voltage signal)

Vg Voltage (gate voltage of feedback transistor)

Vgosc Voltage (oscillation start value)

Vg1 Voltage (first value)

Vg2 Voltage (second value)

Vgp Voltage (third value)

1. An amplifier provided in a photon-counting radiation detector, theamplifier comprising: an inverting amplification unit that inverts andamplifies an input signal to generate an inverted amplified output; afeedback transistor that connects an input unit and an output unit ofthe inverting amplification unit to each other; and a pulse measurementunit that generates an output signal corresponding to a number of pulsesof the inverted amplified output, wherein the pulse measurement unit iscapable of supplying the output signal toward the feedback transistor.2. The amplifier according to claim 1, further comprising a switch thatswitches a supply destination of the output signal from the pulsemeasurement unit either (i) toward the feedback transistor or (ii) tothe outside of the amplifier.
 3. The amplifier according to claim 1,wherein in a case where the pulse measurement unit supplies the outputsignal toward the feedback transistor, the pulse measurement unit isconnected to a gate of a second transistor, the second transistor isconnected to a gate of the feedback transistor through a thirdtransistor, at a point in time before the inverting amplification unitoscillates, the second transistor and the third transistor are switchedon and a gate voltage of the feedback transistor increases according toa second voltage signal supplied to the second transistor, at a point intime when the gate voltage of the feedback transistor reaches anoscillation start value, the inverting amplification unit starts tooscillate, at a point in time after the inverting amplification unitstarts to oscillate, the gate voltage of the feedback transistor is heldat a first value larger than the oscillation start value by switchingoff the second transistor as the oscillation of the invertingamplification unit continues, and at a point in time after the gatevoltage of the feedback transistor is held at the first value, the gatevoltage of the feedback transistor is held at a second value smallerthan the oscillation start value by extracting electric charge from thefeedback transistor in accordance with a change in a third voltagesignal supplied to the third transistor.
 4. The amplifier according toclaim 3, further comprising a capacitor, wherein one terminal of thecapacitor is connected to the feedback transistor through the thirdtransistor, a fourth voltage signal is supplied to another terminal ofthe capacitor, and at the point in time after the gate voltage of thefeedback transistor is held at the first value, the gate voltage of thefeedback transistor is held at a third value smaller than theoscillation start value by extracting electric charge from the feedbacktransistor in accordance with a change in the fourth voltage signal. 5.A radiation detector comprising: the amplifier according to claim 1; anda sensor element that generates the input signal according to a dose ofradiation incident on the sensor element.
 6. The radiation detectoraccording to claim 5, wherein the radiation detector includes: aplurality of amplifiers each of which is the amplifier; and one or morevoltage sweep units that output a second voltage signal increasing agate voltage of the feedback transistor at a point in time before theinverting amplification unit oscillates, and two or more amplifiers ofthe plurality of the amplifiers share one of the one or more voltagesweep units with each other.
 7. The radiation detector according toclaim 6, wherein all of the plurality of the amplifiers share the onevoltage sweep unit with one another.
 8. A radiation detector controlmethod for controlling the radiation detector according to claim 5, themethod comprising: a first step of operating the radiation detector in afirst mode of counting a number of photons of the radiation to detectthe radiation by switching the supply destination of the output signalfrom the pulse measurement unit toward the feedback transistor; and asecond step of operating the radiation detector in a second mode ofregulating a feedback resistance value of the inverting amplificationunit by switching the supply destination of the output signal from thepulse measurement unit to the outside of the amplifier.
 9. The radiationdetector control method according to claim 8, wherein the second stepincludes: a step of decreasing the feedback resistance value so that theinverting amplification unit is shifted from a state where the invertingamplification unit does not oscillate to a state in which the invertingamplification unit does oscillate; a step of detecting that theinverting amplification unit oscillates by using the pulse measurementunit; a step of holding the feedback resistance value at a firstfeedback resistance value at which the oscillation of the invertingamplification unit continues; and a step of increasing the feedbackresistance value from the first feedback resistance value to a secondfeedback resistance value at which the oscillation of the invertingamplification unit does not occur and holding the second feedbackresistance value.